1. Field of the Invention
The present invention relates to a dental astral lamp which is an accessory of dental treating equipment and can make an appropriate compromise between opposite demands i.e., a luminous intensity so high for usual dental treatments that it can make it easy for a dentist to carry out precise manipulations for cutting the teeth of a patient and a combination of a color temperature with a low luminous intensity which can make it easy for a dentist to select artificial teeth and fillers in good agreement with the color of the teeth of a patient.
2. Statement of the Prior Art
In general, cutting of decayed teeth of a patient and filling of a filler into a decayed portion constitute a major part in dental treatments. Thus, a light source of a considerably strong luminous intensity is needed to carry out such treatments, since the portion to be treated is of a very small area. For that reason usually employed to this end is a dental astral lamp using a tungsten halogen lamp as its light source.
Such a dental astral lamp using a tungsten halogen lamp as its light source has conventionally a luminous intensity of the order of 15,000 to 25,000 luxes and a color temperature of the order of 3,000 to 4,500 kelvins at the focal position.
With the recent remarkable developments in dental treatments, however, the range of treatments have now covered from artificial teeth such as full dentures, partial dentures, bridges or post crowns, treatments for the bonding and fixation of prostheses such as jacket crowns. Not only for such dental treatments but also in the filling of fillers such as composite resins in decayed portions of natural teeth, it has been required to select a material of a color tone well matching with a patient.
In such color matching between natural teeth and artifical teeth, etc., there is a difference in spectral reflectance that is one of the physical characteristics with respect to light due to their differences in material and structure. There is also a difference in spectral energy distribution among general illumination light sources available in zones of life such as sunrays, incandescent lamps and fluorescent lamps. For those reasons, the results of color matching of natural teeth with artificial teeth, etc. vary depending upon what type of light is used for color matching between natural and artificial teeth etc. due to a difference in spectral energy distribution which these light sources have. In other words, the color tone of artificial teeth, etc. subjected to color matching in the light of a white fluorescent lamp or an incandescent lamp gives rise to a color shift larger than tolerance in the light of other fluorescent lamps or sunrays, which is known as the so-called metamerism in chromatics.
In general, the light source used as a reference in the observation of a color should be indirect incident rays of the sun through a northward window during a period of from two hours after sunrise to two hours before sundown. Weather conditions, sites where treatments are carried out, treating time or other factors, however, will not always guarantee sunrays on fine day. As a result, it is often required that color matching be carried out in the light of an artificial light source.
In view of chromatic agreement, it has recently been established that an artificial illuminator having any one color temperature of 5,500 kelvins, 6,500 kelvins and 7,500 kelvins corresponding to daylight be used as a standard illuminator. However, the color temperature of the tungsten halogen lamp used as a light source for white fluorescent lamps for indoor illumination or dental astral lamps built in dental units is of the order of 3,000 to 4,500 luxes as mentioned above, and it is largely different from that of sunrays and is thus low in color rendering properties. Thus, the development of an illuminator to replace sunrays has been desired.
A conventional dental astral lamp using a tungsten halogen lamp as its light source has a luminous intensity of 15,000 to 25,000 luxes at its focal position so as to meet an illumination condition under which precise manipulations such as cutting of teeth can be carried out. However, such a luminous intensity is too strong and therefore not preferred, since the luminous intensity of an illuminator for colorimetry of artificial teeth, etc. is considered to be satisfactory at 2,000 to 3,000 luxes as a reference light source where eyes are adapted to ordinary indoor lightness.
In consequence, it is required for dental treatments that use be made of not only a luminous intensity so strong that precise manipulations such as cutting of teeth can be carried out but also a combination of a luminous intensity of 1,500 to 4,500 luxes and a color temperature of 5,000 to 7,500 kelvins for color matching. However, the treatment needing color matching is still a minor part the overall dental treatment process, and there is often no space for the installation of another light source in relation to the size of a treatment room.